Many technological fields require the attachment of one or more components to a substrate with a precise alignment with respect to each other and the substrate. Electrical or optical signals or power may be transferred from, for example, the substrate to the component or between components. The components may be either electrical or optical devices and may be either active or passive devices. For example, integrated circuit chips must be aligned with respect to circuit boards so that they may be soldered or otherwise connected to an electrically conducting pattern on the circuit board. As another example, optical fibers or lenses must be aligned with respect to each other or with respect to a light source so that light may be transmitted through the fibers or lenses. The devices may then be soldered or otherwise aligned and attached to the substrate. In some instances, both optical and electrical signals or power will be transferred between devices and substrate.
As might be expected, a variety of techniques has been developed to position the two or more components with respect to each other and the substrate. Perhaps the conceptually simplest technique may be termed pick and place. One component is picked up and then placed on the substrate in the proper position with the desired alignment with respect to other components. After components are placed on the substrate, they are permanently attached to, for example, solder bumps on the substrate. Photolithographic techniques are frequently used to define the solder bumps. These techniques are capable of great precision. The simplest pick and place technique is done manually; more sophisticated techniques use machines and are highly automated. The pick and place technique is limited to relatively coarse, that is, imprecise, alignments, of components. Thus, pick and place techniques do not have the accuracy that lithographic techniques can achieve.
Self-aligned techniques have been developed in attempts to overcome the problems described above with respect to the accuracy attainable with pick and place techniques and obtain component alignment more precise than that attainable with pick and place techniques. There is also the expectation that, for a given alignment accuracy, self-aligned techniques will be less expensive than are pick and place techniques. See, for example, U.S. Pat. Nos. 4,558,812 and 5,178,723 issued on Dec. 17, 1985 and Jan. 13, 1993, respectively, to Bailey et, al., (Bailey) and Nguyen, respectively, for descriptions of several self-alignment techniques. Bailey teaches methods for batch solder bumping of chip carriers. According to one embodiment described by Bailey, chip carriers are individually placed in apertures in a holder as they are released from a dispensing means. Solder bumps are located in dimples on a plate and form arrays corresponding to bond pad arrays. The holder is moved so that the carriers contact and are then attached to the solder bumps. In one embodiment, Nguyen teaches forming optical devices in which optical components or elements are placed in indentations in one piece and maintained there by means of vacuum channels which communicate with the indentations. A substrate with indentations for receiving the optical elements is brought into contact with the elements and the elements are then bonded to the substrate.
Although the methods described are perfectly adequate for many applications, a method that directly aligns the components to each other and the substrate would be desirable. Such a method would result in improved accuracy over typical pick and place methods. The method should position the components for solder bump attachment with accuracy attained by the photolithographic process used to define the solder bump rather than by the pick and place process.